The Evolution of HTTP - Understanding HTTP 0.9, HTTP 1.0, HTTP 1.1, HTTP 2 and HTTP 3

February 2, 2025

Hypertext Transfer Protocol (HTTP) is an application-layer protocol for transmitting hypermedia documents, such as HTML pages, text, images, videos, and much more. It was designed for communication between web browsers and web servers, but it can also be used for other purposes, such as machine-to-machine communication, programmatic access to APIs, and more.

HTTP/0.9

Released in 1991.
The request only had one HTTP method, GET, to retrieve a resource using a path.
The response included only an HTML file. There were no HTTP headers, status codes, etc.
To indicate an error, the server would provide an error-specific HTML page in response.

Request:

GET /index.html

Response:

<html>
  Welcome to the example.re homepage!
</html>

HTTP/1.0

Finalized in 1996.
Versioning information was sent within each request (HTTP/1.0 was appended to the GET line).
Introduced multiple HTTP methods:
- HEAD and POST methods were added.
- POST was introduced to send data from client to server.
Introduced the concept of HTTP headers.
Status codes were added to indicate success or failure.
Allowed the transmission of documents other than plain HTML files using the Content-Type header.
In the meantime, proper standardization was in progress alongside HTTP/1.0 implementations.

HTTP/1.1

Published in early 1997 (a few months after HTTP/1.0).
Persistent connections introduced to reuse an HTTP connection instead of opening a new TCP connection for each request.
Keep-alive mechanism added:
- Clients sent the Connection: keep-alive header.
- The server responded with Connection: keep-alive to maintain the connection.
Pipelining introduced to allow sending multiple requests over the same connection without waiting for responses, reducing latency.
Chunked transfer encoding introduced:
- Allowed the server to send data in chunks without knowing the total size beforehand.
- Reduced latency and supported dynamic content generation.
Enhanced cache control mechanisms:
- Added headers like Cache-Control, ETag, and Last-Modified.
Content negotiation introduced:
- Accept: (Type Negotiation)
- Accept-Language: (Language Negotiation)
- Accept-Encoding: (Encoding Negotiation)
Host header introduced, allowing multiple domains on a single IP address (Server colocation).

Example HTTP/1.1 Request:

GET /api/products HTTP/1.1
Host: www.example.com
User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64)
Accept: application/json
Accept-Encoding: gzip, deflate
Accept-Language: en-US, fr;q=0.8
Cache-Control: max-age=3600
Connection: keep-alive

Example HTTP/1.1 Response:

HTTP/1.1 200 OK
Date: Wed, 30 Jan 2025 12:34:56 GMT
Server: Apache/2.4.41 (Ubuntu)
Content-Type: application/json
Content-Encoding: gzip
Transfer-Encoding: chunked
ETag: "abc123etag"
Cache-Control: public, max-age=3600
Vary: Accept-Encoding
Connection: keep-alive

1F
{"id":1,"name":"Laptop"}
14
{"id":2,"name":"Smartphone"}
0

First published as RFC 2068 in January 1997.

Secure Transmission with SSL and TLS

SSL (1994) introduced encryption to HTTP, enabling secure e-commerce.
SSL evolved into TLS, essential for protecting private data.

HTTP for Complex Applications

WebDAV (1996) extended HTTP for document editing, address books, and calendars.
REST (2000s) became the norm for APIs, using standard HTTP methods.
Server-Sent Events (SSE) and WebSockets extended HTTP capabilities for real-time communication.
Security models evolved, introducing headers like CORS, CSP, Do Not Track (DNT), and X-Frame-Options.

HTTP/2

Released in 2015.
The web became more media-rich and interactive, requiring better performance.
Google’s SPDY protocol inspired HTTP/2, which improved latency and security.
Binary protocol: Faster and more efficient than text-based HTTP/1.x.
Header compression to reduce HTTP header size.
Multiplexing: Multiple requests and responses can be sent over a single connection simultaneously.
Better network resource utilization by avoiding multiple TCP connections.
Server push allows sending resources before the client requests them.
Alternative services via the Alt-Svc header for improved routing.
Backward compatible with HTTP/1.1.

HTTP/3

Uses QUIC instead of TCP, making it faster and more reliable.
QUIC reduces latency by handling packet loss better.
QUIC is built on top of UDP, it is not directly affected by the limitations of TCP
Supports multiplexing like HTTP/2 but avoids TCP’s limitations.
Most major browsers support HTTP/3, including Chrome, Edge, and Firefox.